Cardiac arrhythmia is the leading cause of sudden death, particularly, for patients with heart failure. Disappointingly, most current treatments have little or no survival benefits and new therapies are urgently needed. The cardiac calcium release channel (ryanodine receptor type 2, RyR2) is quickly emerging as an important point in the pathogenesis of cardiac arrhythmia. Mutations in RyR2 have been linked to at least 2 forms of cardiac arrhythmias, catecholaminergic polymorphic ventricular tachycardia (CPVT) and arrhythmogenic right ventricular cardiomyopathy type 2 (ARVD2). Defective RyR2 channel function has also been implicated in drug-induced cardiac arrhythmia. Our goal is to define the actions of disease-causing RyR2 mutations and of RyR2-interacting pro- and anti-arrhythmic agents, and the molecular mechanism of channel function that mediates their actions, thereby providing the knowledge basis necessary for the development of effective anti-arrhythmic therapies. 3 specific aims are proposed. 1. Define the functional consequences of CPVT RyR2 mutations. The functional impacts of CPVT mutations on RyR2 channel function will be investigated at the whole cell, molecular and single channel levels. 2. Understand the molecular actions of RyR2-interacting pro- and anti-arrhythmic agents. The impacts of RyR2-interacting pro- and anti-arrhythmic agents on RyR2 channel function will be assessed by a combination of techniques including single cell calcium imaging, single channel analysis and radioligand binding. 3. Define the molecular basis of calcium regulation of the RyR2 channel. Site-directed mutagenesis in conjunction with single channel analysis will be employed to systematically define the role of the channel pore region in calcium activation of the RyR2 channel. These studies will shed novel and important insight into the causal mechanisms of RyR2-associated cardiac arrhythmias and sudden death, and will have profound implications to the treatment of cardiac arrhythmias arising from various cardiac diseases including heart failure.